1. Field of the Invention
This invention relates generally to anemometer sensing apparatus for determining the motion of a fluid mass which surrounds the transducer or, conversely, motion of the transducer through the fluid. The invention is particularly concerned with a directional heat loss anemometer transducer for sensing both the speed and direction of motion of a fluid, as a liquid or a gas, in which the transducer is immersed.
2. Description of the Prior Art
It is known in the anemometer sensing apparatus art to employ hot wire and hot film anemometer transducers. Examples of prior art thermal anemometer sensors, and circuits therefor, are shown in U.S. Pat. Nos. 3,138,025, 3,333,470, 3,352,154, 3,604,261, 3,900,819 and 4,024,761. The present invention overcomes several disadvantages or deficiencies which are found in the prior art anemometer sensors.
Two significant deficiencies which may be observed to be characteristic of the prior art transducers are their relative insensitivity at low flow angles which are parallel or nearly parallel to the transducer's major dimensional axis, and their susceptibility to dissimilarities of speed response from side to side. An ideal transducer will exhibit clean smooth axis crossings when the transducer's polar response characteristic is displayed or graphically plotted. Prior art transducers often rely on artifices such as the introduction of electrical "dither" signals to aid in lobe switching from side to side. This in effect provides a "synthetic" speed signal through the axis crossing region rather than a signal which is truly derived from the direction transducer itself.